Battery current sensing is often used for predicting the state of the charge (SoC) of the battery. Sensing the battery current correctly is the key to obtain the remaining capacity of the battery. However, the battery current varies usually from milliamps to amps range, for example, 1 mA to 2 A. With a constant sensing resistor (5-20 mohm) upon which the battery current flowing through, the sensing voltage across the sending resistor varies from several μV to tens of mV, wherein the μV level voltage with high accuracy demand is a difficult challenge for signal process and IC design.
Another conventional way to estimate the remaining capacity of battery is to measure the open circuit voltage of the battery, while the sensing for the mA level current is ignored. However, the relationship between the open circuit voltage of the battery and the remaining capacity is difficult to determine under the different loads, temperatures, charging/discharging rate as well as charging/discharging cycles. And more, a complex and extra compensation circuit for special application is needed for precise fuel gauging.